Amine recovery method and apparatus and decarbonation apparatus having same

ABSTRACT

In a decarbonation process for removing carbon dioxide from a carbon dioxide-containing gas with the use of an amine compound-containing absorbing solution, an amine compound accompanying a decarbonated exhaust gas is efficiently recovered in the following manner: A water washing section is constituted in two stages, a first-stage water washing section  64  and a second-stage water washing section  65 . In these water washing sections, recovery of the amine compound accompanying the decarbonated exhaust gas is performed sequentially. Regeneration tower refluxed water is supplied as washing water to the second-stage water washing section  65 . Washing water is withdrawn from the second-stage water washing section  65  and supplied to the first-stage water washing section  64 . Demisters  83, 84  and  85  are provided at outlets of a carbon dioxide absorption section  73 , the first-stage water washing section  64  and the second-stage water washing section  65 . An absorbing solution mist and a washing water mist accompanying the decarbonated exhaust gas are removed by these demisters.

TECHNICAL FIELD

[0001] This invention relates to an amine recovery method and apparatus,and a decarbonation apparatus having the amine recovery apparatus.

BACKGROUND ART

[0002] In recent years, thermal power equipment and boiler equipmenthave used large amounts of coal, heavy oil or superheavy oil as fuels.From the points of view of air pollution control and Earth environmentpurification, it has become problems how to decrease the quantities andconcentrations of emissions of sulfur oxides (mainly sulfur dioxide),nitrogen oxides, and carbon dioxide. Suppression of carbon dioxideemission, in particular, has recently been investigated, together withemission control of flon gas and methane gas, from the viewpoint ofglobal warming. For this purpose, methods for removing carbon dioxide,such as PSA (pressure swing) method, membrane separation, and absorptionby reaction with basic compounds, are under study.

[0003] As an example of a method for removing carbon dioxide with theuse of basic compounds, Japanese Unexamined Patent Publication No.1993-184866 (related U.S. Pat. No. 5318758) proposes a method whichperforms decarbonation by using an aqueous solution of an amine compound(hereinafter referred to simply as an amine) as a solution for absorbingcarbon dioxide. In this method, the reaction between carbon dioxide andthe amine compound is an exothermic reaction. Thus, the temperature ofthe absorbing solution in a carbon dioxide absorption section rises toraise the vapor pressure of the amine. That is, the amine-containingabsorbing solution evaporates owing to the temperature increase. As aresult, the amount of the amine compound accompanying a decarbonated gasincreases. Thus, a water washing section is provided in an absorptiontower, and the decarbonated gas and washing water are subjected tovapor-liquid contact in the water washing section, whereby the aminecompound accompanying the decarbonated gas is recovered into a liquidphase.

[0004] Concretely, the above-mentioned Japanese Unexamined PatentPublication No. 1993-184866 discloses a decarbonation apparatus as shownin FIGS. 2 and 3.

[0005] In FIG. 2, the reference numeral 1 denotes an absorption tower, 2a carbon dioxide absorption section, 3 a water washing section, 4 anexhaust gas supply section, 6 is an absorbing solution supply port, 7 anozzle, 8 a liquid reservoir in the water washing section, 9 acirculating pump, 10 a cooler, 11 a nozzle, 12 an absorbing solutiondischarge port, 13 a blower, 14 an exhaust gas supply port, 15 anexhaust gas cooler, 16 a circulating pump, 17 a cooler, 18 a nozzle, and19 a drainage line.

[0006] Although a detailed explanation is omitted, a combustion exhaustgas supplied through the exhaust gas supply port 14 is cooled by thecooling tower 15, and then fed to the absorption tower 1. In the carbondioxide absorption section 2 of the absorption tower 1, the fedcombustion exhaust gas is brought into countercurrent contact with anabsorbing solution supplied through the absorbing solution supply portvia the nozzle 7. As a result, carbon dioxide in the combustion exhaustgas is absorbed and removed by the absorbing solution. The loadedabsorbing solution, which has absorbed carbon dioxide, is sent to aregeneration tower (not shown) through the absorbing solution dischargeport 12. In the regeneration tower, the loaded absorbing solution isregenerated, and fed again from the absorbing solution supply port 16 tothe absorption tower 1.

[0007] On the other hand, the combustion exhaust gas decarbonated in thecarbon dioxide absorption section (i. e., decarbonated exhaust gas)ascends, accompanied by a large amount of an amine vapor, due to atemperature rise ascribed to an exothermic reaction between carbondioxide and an amine compound in the carbon dioxide absorption section2. The ascending decarbonated exhaust gas passes through the liquidreservoir 8, and heads toward the water washing section 3. In the waterwashing section 3, reserved water in the liquid reservoir 8 istransported by the circulating pump 9, cooled by the cooler 10, and thensupplied to the water washing section 3 as washing water through thenozzle 11. As a result, this washing water and the decarbonated exhaustgas make countercurrent contact in the water washing section 3, wherebythe amine compound in the decarbonated exhaust gas is recovered into theliquid phase.

[0008]FIG. 3 is characterized by improving the amine recovering abilityby utilization of regeneration tower refluxed water. In FIG. 3, thereference numeral 21 denotes an absorption tower, 22 a carbon dioxideabsorption section, 23 a water washing section, 24 an exhaust gas supplyport, 25 an exhaust gas discharge port, 26 an absorbing solution supplyport, 27 a nozzle, 28 a regeneration tower ref luxed withdrawn watersupply port, 29 a nozzle, 30 a cooler, 31 a nozzle, 32 a chargingsection, 33 a circulating pump, 34 a make-up water supply line, 35 anabsorbing solution discharge pump, 36 a heat exchanger, 37 a cooler, 38a regeneration tower, 39 a nozzle, 40 a lower charging section, 41 areboiler, 42 an upper charging section, 43 a refluxed water pump, 44 acarbon dioxide separator, 45 a carbon dioxide discharge line, 46 acooler, 47 a nozzle, 48 a ref luxed water supply line, and 49 acombustion gas supply blower.

[0009] Although a detailed explanation is omitted, a combustion exhaustgas supplied by the combustion gas supply blower 49 is cooled by thecooling tower 30, and then fed to the absorption tower 21. In the carbondioxide absorption section 22 of the absorption tower 21, the fedcombustion exhaust gas is brought into countercurrent contact with anabsorbing solution supplied through the absorbing solution supply port26 via the nozzle 27. As a result, carbon dioxide in the combustionexhaust gas is absorbed and removed by the absorbing solution. Theloaded absorbing solution, which has absorbed carbon dioxide, is sent tothe regeneration tower 38 by the absorbing solution discharge pump 35through the absorbing solution discharge port 12. In the regenerationtower 38, the loaded absorbing solution is regenerated, and fed again tothe absorption tower 21 through the absorbing solution supply port 26.

[0010] On the other hand, the combustion exhaust gas decarbonated in thecarbon dioxide absorption section 22 (i.e., decarbonated exhaust gas)ascends, accompanied by a large amount of an amine vapor, owing to atemperature rise ascribed to an exothermic reaction between carbondioxide and an amine compound in the carbon dioxide absorption section22. The ascending decarbonated exhaust gas heads toward the waterwashing section 23. In the water washing section 23, part ofregeneration tower refluxed water withdrawn as washing water is suppliedto the water washing section 23 through the regeneration tower ref luxedwithdrawn water supply port 28 via the nozzle 29. As a result, thiswashing water and the decarbonated exhaust gas make countercurrentcontact in the water washing section 23, whereby the amine compound inthe decarbonated exhaust gas is recovered into the liquid phase.

[0011] However, according to the above-described conventionaldecarbonation apparatus shown in FIG. 2, in particular, the waterwashing section is provided as one stage. Thus, the concentration ofamine recovered by the washing water is so high that the recovery ofamine is insufficient. As a result, amine accompanies the decarbonatedexhaust gas, and is released to the outside of the decarbonation processsystem. Consequently, amine is wasted, causing a concern about anincrease in the operating cost, etc.

[0012] The present invention has been accomplished in the light of theforegoing problems. Its object is to provide an amine recovery methodand apparatus, and a decarbonation apparatus equipped with the aminerecovery apparatus, the amine recovery method and apparatus beingcapable of efficiently recovering an amine compound accompanying adecarbonated exhaust gas in a decarbonation process in which carbondioxide is removed from a gas containing carbon dioxide with the use ofan amine compound-containing absorbing solution.

DISCLOSURE OF THE INVENTION

[0013] An amine recovery method as a first invention for solving theabove problems is an amine recovery method for recovering an aminecompound accompanying a decarbonated exhaust gas by bringing thedecarbonated exhaust gas into vapor-liquid contact with washing water ina water washing section, the decarbonated exhaust gas having had carbondioxide absorbed and removed by vapor-liquid contact with an absorbingsolution containing the amine compound in a carbon dioxide absorptionsection, characterized in that

[0014] the water washing section is constituted in a plurality ofstages, and

[0015] recovery of the amine compound accompanying the decarbonatedexhaust gas is performed sequentially in the water washing sections inthe plural stages.

[0016] Thus, according to the amine recovery method as the firstinvention, the water washing section is constituted in a plurality ofstages, and recovery of the amine compound accompanying the decarbonatedexhaust gas is performed sequentially in the water washing sections inthe plural stages. Consequently, the amine compound accompanying thedecarbonated exhaust gas can be recovered very efficiently, and theoperating cost can be reduced.

[0017] An amine recovery method as a second invention is the aminerecovery method of the first invention, characterized in that

[0018] regeneration tower refluxed water is supplied as washing water tothe water washing section.

[0019] Thus, according to the amine recovery method of the secondinvention, the concentration of amine contained in washing water of thewater washing section is decreased, and the amine recovery ability isfurther enhanced.

[0020] An amine recovery method as a third invention is the aminerecovery method of the first or second invention, characterized in that

[0021] washing water is withdrawn from the water washing section in thesucceeding stage and supplied to the water washing section in thepreceding stage.

[0022] Thus, according to the amine recovery method of the thirdinvention, the concentration of amine contained in washing water of thewater washing section in the preceding stage is decreased to enhance theamine recovery ability in the water washing section in the precedingstage. In accordance with this advantage, the concentration of aminecontained in washing water of the water washing section in thesucceeding stage is also further decreased to further enhance the aminerecovery ability as a whole.

[0023] An amine recovery method as a fourth invention is the aminerecovery method of the first, second or third invention, characterizedin that

[0024] demisters are provided at outlets of the carbon dioxideabsorption section and the water washing sections in the respectivestages, and

[0025] an absorbing solution mist and a washing water mist accompanyingthe decarbonated exhaust gas are removed by the demisters.

[0026] Thus, according to the amine recovery method of the fourthinvention, it can be prevented that part of the absorbing solution mistfed to the carbon dioxide absorption section and part of the washingwater mist fed to the water washing sections in the respective stagesare released to the outside of the system together with the decarbonatedexhaust gas, causing losses in water and amine compound.

[0027] An amine recovery apparatus as a fifth invention is an aminerecovery apparatus for recovering an amine compound accompanying adecarbonated exhaust gas by bringing the decarbonated exhaust gas intovapor-liquid contact with washing water in a water washing section, thedecarbonated exhaust gas having had carbon dioxide absorbed and removedby vapor-liquid contact with an absorbing solution containing the aminecompound in a carbon dioxide absorption section, characterized in that

[0028] the water washing section is constituted in a plurality ofstages, and

[0029] recovery of the amine compound accompanying the decarbonatedexhaust gas is performed sequentially in the water washing sections inthe plural stages.

[0030] Thus, according to the amine recovery apparatus of the fifthinvention, the water washing section is constituted in a plurality ofstages, and recovery of the amine compound accompanying the decarbonatedexhaust gas is performed sequentially in the water washing sections inthe plural stages. Consequently, the amine compound accompanying thedecarbonated exhaust gas can be recovered very efficiently, and theoperating cost can be reduced.

[0031] An amine recovery apparatus as a sixth invention is the aminerecovery apparatus of the fifth invention, characterized in that

[0032] regeneration tower refluxed water is supplied as washing water tothe water washing section.

[0033] Thus, according to the amine recovery apparatus of the sixthinvention, the concentration of amine contained in washing water of thewater washing section is decreased, and the amine recovery ability isfurther enhanced.

[0034] An amine recovery apparatus as a seventh invention is the aminerecovery apparatus of the fifth or sixth invention, characterized inthat

[0035] washing water is withdrawn from the water washing section in thesucceeding stage and supplied to the water washing section in thepreceding stage.

[0036] Thus, according to the amine recovery apparatus of the seventhinvention, the concentration of amine contained in washing water of thewater washing section in the preceding stage is decreased to enhance theamine recovery ability in the water washing section in the precedingstage. In accordance with this advantage, the concentration of aminecontained in washing water of the water washing section in thesucceeding stage is also further decreased to further enhance the aminerecovery ability as a whole.

[0037] An amine recovery apparatus as an eighth invention is the aminerecovery apparatus of the fifth, sixth or seventh invention,characterized in that

[0038] demisters are provided at outlets of the carbon dioxideabsorption section and the water washing sections in the respectivestages, and

[0039] an absorbing solution mist and a washing water mist accompanyingthe decarbonated exhaust gas are removed by the demisters.

[0040] Thus, according to the amine recovery apparatus of the eighthinvention, it can be prevented that part of the absorbing solution mistfed to the carbon dioxide absorption section and part of the washingwater mist fed to the water washing sections in the respective stagesare released to the outside of the system together with the decarbonatedexhaust gas, causing losses in water and amine compound.

[0041] A decarbonation apparatus as a ninth invention is characterizedby having the amine recovery apparatus of the fifth, sixth, seventh oreighth invention in an absorption tower.

[0042] Thus, the decarbonation apparatus of the ninth invention has theamine recovery apparatus of the fifteenth, sixth, seventh or eighthinvention in an absorption tower. Hence, the decarbonation apparatus isan apparatus with a high ability to recover the amine compound andinvolving a low operating cost.

BRIEF DESCRIPTION OF THE DRAWINGS

[0043]FIG. 1 is a configuration drawing showing a main portion of adecarbonation apparatus according to an embodiment of the presentinvention.

[0044]FIG. 2 is a configuration drawing showing a main portion of aconventional decarbonation apparatus.

[0045]FIG. 3 is a configuration drawing showing a main portion of aconventional decarbonation apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

[0046] An embodiment of the present invention will now be described indetail based on the accompanying drawings.

[0047]FIG. 1 is a configuration drawing showing a main portion of adecarbonation apparatus according to the embodiment of the presentinvention. As shown in FIG. 1, the decarbonation apparatus of thepresent embodiment has an absorption tower 61, a regeneration tower 62,and a cooling tower 63.

[0048] Although details will be described later, the decarbonationapparatus of the present embodiment is characterized in that a waterwashing section of the absorption tower 61 has a two-stage structure,i.e., a first-stage water washing section 64 and a second-stage waterwashing section 65; that washing water of the second-stage water washingsection 65 is withdrawn and supplied to the first-stage water washingsection 64; that regeneration tower ref luxed water is supplied aswashing water to the second-stage water washing section; and thatdemisters 83, 84 and 85 are installed at outlets of a carbon dioxideabsorption section 73, the first-stage water washing section 64 and thesecond-stage water washing section 65.

[0049] In detail, a combustion exhaust gas generated in thermal powerequipment or boiler equipment is supplied to the cooling tower 63 via anexhaust gas supply line 66. Water is stored at the bottom 67 of thecooling tower 63. This water is scooped up by a circulating pump 68,cooled by a heat exchanger 69, and then supplied to a charging section71 through a nozzle 70. As a result, the combustion exhaust gas iscooled in the charging section 71 upon countercurrent contact withcooling water diffused from the nozzle 70. Then, the combustion exhaustgas is supplied through an exhaust gas supply line 72 to the carbondioxide absorption section 73 provided in a lower portion of theabsorption tower 61.

[0050] The combustion exhaust gas supplied to the absorption tower 61ascends within the absorption tower as indicated by dotted arrows in thedrawing. On the other hand, a regenerated absorbing solution (an aqueoussolution of an amine compound) reserved at the bottom 76 of theregeneration tower 62 is transported by an absorbing solution supplypump 77 provided in an absorbing solution supply line 74. Thetransported regeneration absorbing solution is cooled by a heatexchanger 78 and a heat exchanger 79, and then supplied to the carbondioxide absorption section 73 through a nozzle 75 provided at the outletof the carbon dioxide absorption section 73. As a result, the combustionexhaust gas and the absorbing solution make vapor-liquid contact(countercurrent contact) in the carbon dioxide absorption section 73.Thus, carbon dioxide contained in the combustion exhaust gas is absorbedinto the absorbing solution and removed thereby.

[0051] Examples of the amine compound contained in the absorbingsolution are alcoholic hydroxyl group-containing primary amines such asmonoethanolamine and 2-amino-2-methyl-1-propanol, alcoholic hydroxylgroup-containing secondary amines such as diethanolamine and2-methylaminoethanol, alcoholic hydroxyl group-containing tertiaryamines such as triethanolamine and N-methyldiethanolamine,polyethylenepolyamines such as ethylenediamine, triethylenediamine anddiethylenetriamine, cyclic amines such as piperazines, piperidines andpyrrolidines, polyamines such as xylylenediamine, amino acids such asmethylaminocarboxylic acid, and mixtures of them. Any of these amines isused usually as 10 to 70% by weight of an aqueous solution. To theabsorbing solution, carbon dioxide absorption promoters or corrosioninhibitors may be added, and methanol, polyethylene glycol and sulfolanemay be added as other media.

[0052] The loaded absorbing solution, which has absorbed carbon dioxide,flows downward, and is stored at the bottom 80 of the absorption tower.Then, the stored solution is discharged by an absorbing solutiondischarge pump 87 provided in an absorbing solution discharge line 86,and is heated upon heat exchange with the regenerated absorbing solutionin the heat exchanger 78. Then, the heated solution is diffused from anozzle 89 provided at the outlet of a lower charging section 88 of theregeneration tower 62, flows down the lower charging section 88, and isstored at the bottom 76 of the regeneration tower.

[0053] The loaded absorbing solution stored at the bottom 76 of theregeneration tower is heated to, for example, about 120° C. by feedsteam in a reboiler 90. As a result, carbon dioxide in the loadedabsorbing solution is released to regenerate the absorbing solution.This regenerated absorbing solution is stored at the bottom 76 of theregeneration tower, and supplied again to the carbon dioxide absorptionsection 73 of the absorption tower 61. That is, the absorbing solutionis used in a circulated manner, and need not be discharged to theoutside or supplied from the outside, unless any loss occurs. On theother hand, the carbon dioxide released ascends as indicated by dottedarrows in the drawing, passes through the lower charging section 88 andan upper charging section 91, and is discharged to the outside of theregeneration tower through a carbon dioxide discharge line 93 at the top111 of the regeneration tower.

[0054] Since the carbon dioxide at this time contains moisture, it iscooled by a condenser (cooler) 94 provided in the carbon dioxidedischarge line 93 to condense moisture contained in the carbon dioxide.The resulting condensate and carbon dioxide are separated by a carbondioxide separator 95. High purity carbon dioxide separated from thecondensate is released to the outside of the decarbonation processsystem (hereinafter referred to simply as the outside of the system)through a carbon dioxide release line 96, and is utilized in asubsequent step or disposed of. The condensate is transported by acirculating pump 96, and part of it is withdrawn toward a regenerationtower refluxed water supply line 97. This regeneration tower refluxedwithdrawn water is cooled by a heat exchanger 98, and then supplied aswashing water to the top of the second-stage water washing section 65through a nozzle 99 provided at the outlet of the second-stage waterwashing section 65. This regeneration tower refluxed withdrawn water hasa very low amine concentration. The remainder of the condensate is refluxed to the regeneration tower 62. That is, it is supplied to the topof the upper charging section 91 through a nozzle 92 via a reflux line100, flowed downward, and reserved at the bottom 76 of the regenerationtower.

[0055] On the other hand, the combustion exhaust gas deprived of carbondioxide (i. e., decarbonated exhaust gas) in the carbon dioxideabsorption section 73 of the absorption tower 61 passes through thedemister 83 provided at the outlet of the carbon dioxide absorptionsection 73, and flows into the first-stage water washing section 64. Atthis time, the decarbonated exhaust gas is accompanied by a large amountof an amine vapor. That is, the temperature rises because of theexothermic reaction between carbon dioxide and the amine compound in thecarbon dioxide absorption section 73, so that a large amount of theabsorbing solution evaporates, ascending together with the decarbonatedexhaust gas. The moisture accompanying the decarbonated exhaust gas atthis time becomes a supply source for washing water in the water washingsection to be described later. The temperature of the decarbonatedexhaust gas, flowing into the first-stage water washing section 64, isabout 50 to 80° C., for example.

[0056] The demister 83 removes a mist of the absorbing solutionaccompanying the decarbonated exhaust gas. That is, the absorbingsolution is diffused from the nozzle 75 as a mist, and part of thisabsorbing solution mist accompanies the decarbonated exhaust gas andascends. If the absorbing solution mist is released, unchanged, to theoutside of the absorption tower along with the decarbonated exhaust gas,there will be a loss of the amine compound. Thus, the demister 83 isprovided at the outlet of the carbon dioxide absorption section toremove the absorbing solution mist accompanying the decarbonated exhaustgas. The moisture (absorbing solution) removed by the demister 83 flowsdownward, and is reserved at the bottom 88 of the absorption tower.

[0057] In the first-stage water washing section 64, reserved water in aliquid reservoir 81 in the first-stage water washing section 64 istransported by a circulating pump 102 provided in a circulation line101. The transported water is cooled by a heat exchanger 103, and thensupplied as washing water to the top of the first-stage water washingsection 64 through a nozzle 104 provided at the outlet of thefirst-stage water washing section 64. As a result, the washing water andthe decarbonated exhaust gas make countercurrent contact in thefirst-stage water washing section 64. Consequently, the temperature ofthe decarbonated exhaust gas lowers, whereupon a water vaporaccompanying the decarbonated exhaust gas condenses. Also, the aminecompound accompanying the decarbonated exhaust gas is recovered. Theresulting condensate and the diffused washing water flow downward, andare stored in the liquid reservoir 81.

[0058] The reserved water in the liquid reservoir 81 is maintained at aconstant water level. That is, when the reserved water in the liquidreservoir 81 increases and reaches more than the constant water level,the reserved water is overflowed to the bottom 80 of the absorptiontower via a reserved water discharge line 105. The reserved water in theliquid reservoir 81 may be transported to the bottom 80 of theabsorption tower by a pump.

[0059] Most of the amine compound accompanying the decarbonated exhaustgas is recovered in the first-stage water washing section 64. At thistime, the amine concentration of the reserved water (washing water) inthe liquid reservoir 81 is high. Thus, the amine vapor pressure becomesso high because of vapor-liquid equilibrium that the amine concentrationin the decarbonated exhaust gas cannot be decreased any further. Thatis, the single-stage water washing section alone cannot fully decreasethe amine concentration in the decarbonated exhaust gas. In the presentembodiment, therefore, the water washing section has a two-stagestructure, the first-stage water washing section 64 and the second-stagewater washing section 65. The decarbonated exhaust gas having aminerecovered in the first-stage water washing section 64 passes through thedemister 84 provided at the outlet of the first-stage water washingsection 64, and flows to the second-stage water washing section 65.

[0060] The demister 84 removes a mist of the washing water accompanyingthe decarbonated exhaust gas. That is, the washing water is diffusedfrom the nozzle 104 as a mist, and part of this washing water mistaccompanies the decarbonated exhaust gas and ascends. If the washingwater mist is released, unchanged, to the outside of the absorptiontower along with the decarbonated exhaust gas, there will be a loss ofthe amine compound. Thus, the demister 84 is provided at the outlet ofthe first-stage water washing section to remove the washing water mistaccompanying the decarbonated exhaust gas. The moisture (washing water)removed by the demister 83 flows downward, and is reserved in the liquidreservoir 81.

[0061] In the second-stage water washing section 65, reserved water in aliquid reservoir 82 in the second-stage water washing section 65 istransported by a circulating pump 107 provided in a circulation line106. The transported water is cooled by the heat exchanger 98, and thensupplied as washing water to the top of the second-stage water washingsection 65 through the nozzle 99 provided at the outlet of thesecond-stage water washing section 65. The regeneration tower refluxedwithdrawn water supplied from the regeneration tower also merges intothis washing water. As a result, the combined washing water and thedecarbonated exhaust gas make countercurrent contact in the second-stagewater washing section 65. Consequently, the amine compound accompanyingthe decarbonated exhaust gas is recovered.

[0062] Most of the amine compound accompanying the decarbonated exhaustgas is recovered in the first-stage water washing section 64. In thesecond-stage water washing section 65, therefore, the amineconcentration of the liquid reservoir 82, namely, the concentration ofthe amine contained in the washing water supplied through the nozzle 99,is kept very low. Thus, in the second-stage water washing section 65,the amine concentration in the decarbonated exhaust gas is fullydecreased because of vapor-liquid equilibrium. That is, in thesecond-stage water washing section 65, the amine compound can be furtherrecovered from the decarbonated exhaust gas released from thefirst-stage water washing section 64, so that the amine concentration inthe decarbonated exhaust gas can be fully decreased.

[0063] Furthermore, washing water in the second-stage water washingsection 65 is withdrawn and supplied to the first-stage water washingsection 64. Concretely, part of the reserved water (washing water) inthe liquid reservoir 82 is withdrawn, and supplied to the liquidreservoir 81 of the first-stage water washing section 64. That is, thereserved water in the liquid reservoir 82 is maintained at a constantwater level. When the reserved water in the liquid reservoir 82increases and reaches higher than the constant water level, the reservedwater is overflowed to the liquid reservoir 81 via a reserved waterdischarge line 108. However, this mode is not restrictive, and thereserved water (washing water) in the liquid reservoir 82 may besupplied to the liquid reservoir 81 by a pump.

[0064] The decarbonated exhaust gas having amine recovered in thesecond-stage water washing section 65 passes through the demister 85provided at the outlet of the second-stage water washing section 65, andis released to the outside of the system through a gas release line 110at the top 109 of the absorption tower. The amine concentration in thedecarbonated exhaust gas released to the outside of the system is a verylow value.

[0065] The demister 85 removes a mist of the washing water accompanyingthe decarbonated exhaust gas. That is, the washing water is diffusedfrom the nozzle 99 as a mist, and part of this washing water mistaccompanies the decarbonated exhaust gas and ascends. If the washingwater mist is released, unchanged, to the outside of the absorptiontower along with the decarbonated exhaust gas, there will be a loss ofthe amine compound. Thus, the demister 85 is provided at the outlet ofthe second-stage water washing section to remove the washing water mistaccompanying the decarbonated exhaust gas. The moisture removed by thedemister 85 flows downward, and is reserved in the liquid reservoir 82.

[0066] The cooling ability of the heat exchanger 98, for example, isadjusted so that the amount of moisture brought from the exhaust gassupply line 72 into the absorption tower together with the combustionexhaust gas, and the amount of moisture brought through the gas releaseline 110 to the outside of the absorption tower together with thecombustion exhaust gas are made equal to maintain water balance. Thismeasure makes water discharge to the outside or water supply from theoutside unnecessary unless there is a loss.

[0067] Moreover, the cooling ability of the heat exchanger 98 and so onare adjusted so that the temperature of the decarbonated exhaust gasreleased through the gas release line 110 is equal to the temperature atthe inlet of the second-stage water washing section 65. In this case,the temperatures at the outlet and the inlet of the second-stage waterwashing section 65 are equal. Thus, steam in the decarbonated exhaustgas in the second-stage water washing section 65 does not condense, andonly the amount of water corresponding to the regeneration tower refluxed withdrawn water overflows and is fed to the liquid reservoir 81 ofthe first-stage water washing section 64. This mode is not necessarilyrestrictive, and the outlet temperature of the second-stage waterwashing section 65 may be adjusted to be lower than its inlettemperature to cause condensation of moisture in the decarbonatedexhaust gas even in the second-stage water washing section 65. Throughthis means, the amount of the resulting condensate may be adapted tooverflow the liquid reservoir 82 and be supplied to the liquid reservoir81 of the first-stage water washing section 64.

[0068] As described in detail above, according to the presentembodiment, the water washing section has the two-stage structure, i.e.,the first-stage water washing section 64 and the second-stage waterwashing section 65, whereby the decarbonated exhaust gas is subjected toamine recovery in the first-stage water washing section 64, and thenfurther subjected to amine recovery in the second-stage water washingsection 65 as well. Thus, the amine compound accompanying thedecarbonated exhaust gas can be recovered very efficiently, and theoperating cost can be reduced.

[0069] Additionally, if the water washing section remains a one-stagestructure and is given a large height only, recovery performance for theamine compound improves. However, the amine concentration in the washingwater in the water washing section becomes so high that the amineconcentration in the decarbonated exhaust gas cannot be madesufficiently low because of vapor-liquid equilibrium. These facts showthat constructing the water washing section in the two-stage form is avery effective means.

[0070] According to the present embodiment, moreover, washing water inthe second-stage water washing section 65 is withdrawn and supplied tothe first-stage water washing section 64, whereby the concentration ofamine contained in the washing water in the first-stage water washingsection 64 is decreased to enhance the amine recovery ability in thefirst-stage water washing section 64. In accordance with this advantage,the concentration of amine contained in the washing water in thesecond-stage water washing section 65 is further decreased to furtherenhance the amine recovery ability as a whole.

[0071] According to the present embodiment, moreover, regeneration towerrefluxed water is supplied, as washing water, to the second-stage waterwashing section 65, whereby the concentration of amine contained in thewashing water in the second-stage water washing section 65 is furtherdecreased to further enhance the amine recovery ability in thesecond-stage water washing section 65. Furthermore, washing water in thesecond-stage water washing section 65 is withdrawn and supplied to thefirst-stage water washing section 64, whereby the concentration of aminecontained in the washing water in the first-stage water washing section64 is decreased to enhance the amine recovery ability in the first-stagewater washing section 64.

[0072] It is desirable that as described above, regeneration towerrefluxed water is supplied to the second-stage water washing section 65,and washing water in the second-stage water washing section 65 iswithdrawn and supplied to the first-stage water washing section 64.However, this mode is not necessarily restrictive. Instead, regenerationtower refluxed water may be supplied to the second-stage water washingsection 65 and the first-stage water washing section 64 at the sametime.

[0073] According to the present embodiment, moreover, the demisters 83,84 and 85 are installed at the outlets of the carbon dioxide absorptionsection 73, first-stage water washing section 64 and second-stage waterwashing section 65. This means can prevent the situation that part ofthe absorbing solution mist fed to the carbon dioxide absorption section73 and part of the washing water mist fed to each of the first-stagewater washing section 64 and the second-stage water washing section 65are released to the outside of the absorption tower together with thedecarbonated exhaust gas, causing losses in water and amine compound.

[0074] The decarbonation apparatus equipped with the amine recoveryapparatus described above is an apparatus with a high ability to recoverthe amine compound and involving a low operating cost.

[0075] The first-stage water washing section 64 and the second-stagewater washing section 65 may be in a packed tower or in a tower withtrays.

[0076] In the above embodiment, the water washing section is formed asthe two-stage structure. However, this is not necessarily restrictive,and the water washing section may have a structure comprising aplurality of stages not less than three stages. In this case as well,the decarbonated exhaust gas containing an amine compound is subjectedto amine recovery in the water washing section at a preceding stage (astage upstream from a decarbonated exhaust gas flow), and then isfurther subjected to amine recovery in the water washing section at asucceeding stage (a stage downstream from the decarbonated exhaust gasflow). That is, recovery of the amine compound accompanying thedecarbonated exhaust gas is performed sequentially in plural stages ofwater washing sections. In this case, the regeneration tower ref luxedwithdrawn water may be supplied to the water washing section in therearmost stage among the plural-stage water washing sections, andwashing water may be withdrawn from the rearmost-stage water washingsection and supplied to the water washing section in the stage precedingit, further withdrawn from the water washing section in this stage andsupplied to the water washing section preceding to it, and so on.

[0077] In the above embodiment, absorption of carbon dioxide containedin the combustion exhaust gas of fuel is taken as an example forexplanation. However, this is not restrictive, and the carbondioxide-containing gas to be decarbonated may be a process gas such as afuel gas, and other various gases can be applied. The pressure of thecarbon dioxide-containing gas to be decarbonated may be an appliedpressure or an atmospheric pressure, and its temperature may be a lowtemperature or a high temperature, without any restrictions. Thecombustion exhaust gas at atmospheric pressure is preferred.

[0078] [Explanation for concrete experiment examples]

[0079] The present invention will be described concretely by anexperimental example, which in no way limit the present invention.

[0080] <Experimental Example>

[0081] The following experiments were conducted as the method of thepresent invention: 30 Nm³/h of a combustion exhaust gas containing 10%carbon dioxide was supplied to the carbon dioxide absorption section 73of the absorption tower 61, and brought into countercurrent contact withan aqueous solution of an alcoholic hydroxyl group-containing secondaryamine (i.e., an absorbing solution) to absorb carbon dioxide to theaqueous solution. The residual decarbonated exhaust gas was fed to thedemister 83 at the outlet of the carbon dioxide absorption section, thenbrought into countercurrent contact with washing water at a liquid/gasratio of 2.2 l/Nm³ in the first-stage water washing section 64, andpassed through the demister 84 at the outlet of the first-stage waterwashing section. Further, the decarbonated exhaust gas was brought intocountercurrent contact with washing water at a liquid/gas ratio of 2.2l/Nm³ in the second-stage water washing section 65, passed through thedemister 85 at the outlet of the second-stage water washing section, andreleased to the outside of the system. During this procedure, theoperation was performed such that the temperature of the gas at theoutlet of the first-stage water washing section and the temperature ofthe gas at the outlet of the second-stage water washing section wereboth 46° C. Also, regeneration tower ref luxed withdrawn water was fedat 1.1 l/h to the second-stage water washing section 65, while washingwater of the second-stage water washing section 65 was withdrawn andsupplied to the first-stage water washing section 64. As a result, theamine concentration in the decarbonated exhaust gas released from theabsorption tower 61 to the outside of the system was 8 ppm.

[0082] <Comparative Example 1>

[0083] The same procedure as in the above experimental example wasperformed, except that the water washing section was a one-stagestructure, and the regeneration tower refluxed withdrawn water wassupplied to the one-stage water washing section, as the conventionalmethod. As a result, the amine concentration in the decarbonated exhaustgas released from the absorption tower 61 to the outside of the systemwas 25 ppm, a higher value than in the above-mentioned Example.

[0084] <Comparative Example 2>

[0085] The same procedure as in the above experimental example wasperformed, except that the liquid withdrawn from the second-stage waterwashing section (washing water) was not supplied to the first-stagewater washing section 64. As a result, the amine concentration in thedecarbonated exhaust gas released from the absorption tower to theoutside of the system was 11 ppm. This value was sufficiently lowcompared with the above Comparative Example 1, but was higher than inthe above-mentioned experimental example. These findings were able toconfirm the effectiveness of withdrawing washing water of thesecond-stage water washing section 65 and supplying it to thefirst-stage water washing section 64.

[0086] The results of the Experimental Example and Comparative Examples1 and 2 are summarized in [Table 1]. By constituting the water washingsection into the two-stage structure, the concentration of aminereleased to the outside of the system can be made sufficiently low.Also, washing water of the second-stage water washing section 65 iswithdrawn and supplied to the first-stage water washing section 64,whereby the concentration of amine released to the outside of the systemcan be made even lower. TABLE 1 Exp. Comp. Comp. Ex. 1 Ex. 1 Ex. 2First-stage water washing section 2.2 2.2 2.2 liquid/gas ratio (1/Nm³)First-stage water washing section 46 46 46 outlet gas temperature (° C.)Second-stage water washing section 2.2 — 2.2 liquid/gas ratio (1/Nm³)Second-stage water washing section 46 — 46 outlet gas temperature (° C.)Regeneration tower refluxed 1.1 1.1 1.1 withdrawn water flow rate (1/h)Supply of second-stage water washing Yes — No section withdrawn liquidto first- stage water washing section Amine concentration of carbon 8 2511 dioxide absorption tower outlet gas (ppm)

[0087] Industrial Applicability

[0088] As described above, the present invention relates to an aminerecovery method and apparatus, and a decarbonation apparatus equippedwith the amine recovery apparatus. This invention is useful when appliedto recovering an amine compound accompanying a decarbonated exhaust gasin a decarbonation process in which carbon dioxide is removed from a gascontaining carbon dioxide with the use of an amine compound-containingabsorbing solution.

1. An amine recovery method for recovering an amine compoundaccompanying a decarbonated exhaust gas by bringing the decarbonatedexhaust gas into vapor-liquid contact with washing water in a waterwashing section, the decarbonated exhaust gas having had carbon dioxideabsorbed and removed by vapor-liquid contact with an absorbing solutioncontaining the amine compound in a carbon dioxide absorption section,characterized in that the water washing section is constituted in aplurality of stages, and recovery of the amine compound accompanying thedecarbonated exhaust gas is performed sequentially in the water washingsections in the plural stages.
 2. The amine recovery method of claim 1,characterized in that regeneration tower refluxed water is supplied aswashing water to the water washing section.
 3. The amine recovery methodof claim 1 or 2, characterized in that washing water is withdrawn fromthe water washing section in the succeeding stage and supplied to thewater washing section in the preceding stage.
 4. The amine recoverymethod of claim 1, 2 or 3, characterized in that demisters are providedat outlets of the carbon dioxide absorption section and the waterwashing sections in the respective stages, and an absorbing solutionmist and a washing water mist accompanying the decarbonated exhaust gasare removed by the demisters.
 5. An amine recovery apparatus forrecovering an amine compound accompanying a decarbonated exhaust gas bybringing the decarbonated exhaust gas into vapor-liquid contact withwashing water in a water washing section, the decarbonated exhaust gashaving had carbon dioxide absorbed and removed by vapor-liquid contactwith an absorbing solution containing the amine compound in a carbondioxide absorption section, characterized in that the water washingsection is constituted in a plurality of stages, and recovery of theamine compound accompanying the decarbonated exhaust gas is performedsequentially in the water washing sections in the plural stages.
 6. Theamine recovery apparatus of claim 5, characterized in that regenerationtower refluxed water is supplied as washing water to the water washingsection.
 7. The amine recovery apparatus of claim 5 or 6, characterizedin that washing water is withdrawn from the water washing section in thesucceeding stage and supplied to the water washing section in thepreceding stage.
 8. The amine recovery apparatus of claim 5, 6 or 7,characterized in that demisters are provided at outlets of the carbondioxide absorption section and the water washing sections in therespective stages, and an absorbing solution mist and a washing watermist accompanying the decarbonated exhaust gas are removed by thedemisters.
 9. A decarbonation apparatus characterized by having theamine recovery apparatus of claim 5, 6, 7 or 8 in an absorption tower.